1. Field of the Invention
The present invention relates to an enzyme electrode and a method of producing the enzyme electrode.
2. Description of the Related Art
An oxidation-reduction (redox) enzyme transfers electrons between a substrate and a cofactor when the enzyme reacts with the substrate. Therefore, a sensor and a fuel cell utilizing the feature of the enzyme can be realized if those electrons can be transferred to an electrically conductive member.
In many cases, a redox center of the redox enzyme is deeply positioned inside a protein having a three dimensional structure (the redox center is also called an active location or an active site). For that reason, it is generally difficult to efficiently detect electron transfer between the active site and the conductive member.
To overcome such a difficulty, a method has been developed which electrically connects the enzyme and the conductive member by a material called a mediator. The mediator is able to enter the inside of the protein constituting the enzyme. Therefore, when the mediator is positioned near the active site, charges generated during a redox reaction can be transferred to the conductive member through the mediator. In other words, charges generated by an enzyme reaction are detected through the conductive member as a result of diffusion of the mediator taking part in the transfer of electrons with respect to the active site or electron hopping between the mediators.
Japanese Patent Laid-Open No. 8-271472 discloses a technique of introducing ferrocene, which functions as a mediator, to a main body or a side chain of the enzyme by utilizing a covalent bond.
However, the mediator introduced to the enzyme by the technique disclosed in Japanese Patent Laid-Open No. 8-271472 is not controlled with respect to the position to which it is introduced. Hence, the mediator is introduced to a random position within the enzyme.
When the mediator is introduced in such a manner, efficient transfer of charges from the active site is not expected except for the case that ferrocene is casually positioned near the active site. In particular, when the disclosed technique is applied to an enzyme sensor, the concentration of a substrate, i.e., the concentration of a target material to be measured, is required to be exactly sensed and a further improvement is demanded.